invention relates to a compression-ignition internal combustion engine which is adapted to operate with a plurality of fuels, and a novel fuel injection pump means is provided which enables the fuels to be selectively mixed with one another during certain periods of operation of the engine.
In view of present environmental concerns, it has been proposed that internal combustion engines of the future should utilize fuels other than fossil fuels in order to reduce pollutants in the air. Furthermore, such engines would also reduce dependence on imported oil. It has been suggested that alcohol would be a good substitute for fossil fuels since the resources for production of alcohol are readily available. However, the use of a fuel such as alcohol presents certain practical problems such as difficulty in starting an engine, and accordingly, compression-ignition engines have been designed for use with different fuels or with a combination of different fuels. Multi-fuel engines have been developed for use by the military which will operate on various high octane fuels. These engines use very high compression ratios in excess of twenty in order to shorten the delay period of combustion of fuels having poor ignition qualities.
Multi-fuel compression-ignition engines have been designed for buses wherein diesel oil is used mainly for starting the engine and during light load operation, while alcohol is used as the primary fuel after a warm up period. The engine employs a first fuel injection system for the diesel oil and a second independent fuel injection system for the alcohol.
A compression-ignition engine has also been developed including a dual fuel injection system wherein a diesel engine was modified so that alcohol is mixed with the diesel fuel, and up to fifty percent of the diesel fuel could be replaced by alcohol. The injection system was designed so that the relatively low viscosity alcohol is mixed with the diesel oil downstream of the fuel injection pump, whereby the alcohol does not flow through the fuel injection pump.
Fuel injection pumps have long employed a conventional construction known as the BOSCH pump which includes a plunger which reciprocates within a bore formed in a housing. The plunger has a very small tolerance with respect to the bore, and this tight fit is employed to form a seal which prevents escape of the fuel past the plunger when the fuel is under high pressure. This arrangement works effectively with a fuel such as diesel oil which has a relatively high viscosity. However, if a fuel of much lower viscosity such as alcohol passes through the pump, leakage of fuel past the plunger becomes a serious problem. The minimal clearance between the plunger and bore is very expensive to manufacture, and an effective seal is not attainable as a practical matter when dealing with very low viscosity fuels.
Prior art compression-ignition engines have required a fuel with a high cetane number. Additives have been blended into fuels to raise the cetane number. Accordingly, it has been expensive to provide fuels with adequately high cetane number to effectively operate in compression-ignition engines.
It is accordingly a desirable objective to provide a multi-fuel compression-ignition engine which can be utilized in automotive applications and which efficiently operates on fuels with relatively low cetane numbers.